Question

I’d like to get an “ID” attribute of type int with a fixed number of digits and leading zeros if necessary.

So, if this number is, for example, 6 and I enter 1 I would get
000001

Answer 1

XSD doesn’t offer the kind of string manipulation you seem to have in mind here. If you want the ID to have six decimal digits, you can define it to require six decimal digits. Or if you want the user to be able to give a value as “1”, you can define the ID to have at most six digits. But in general, rules of the form “The user enters string X and the system maps that automatically to string Y” are out of scope for XSD.

To figure out how to deal with this situation, ask yourself (and perhaps explain to those reading this question) why you want this kind of string mapping? If it’s to ensure that “1” and “01” and “000001” all map to the same value, then declaring the attribute as integer already does that. If it’s something else (I’m having trouble coming up with alternate motivations), a different solution may be in order.

But now to the question you actually asked.

To define a subtype of xs:integer with exactly six digits in the lexical representation, you can write something like this:

<xs:attribute name="ID">
  <xs:simpleType>
    <xs:restriction base="xs:integer">
      <xs:pattern value=".{6}"></xs:pattern>
    </xs:restriction>
  </xs:simpleType>
</xs:attribute>

Or if (as Sean Kenny suggests in his comment) what you really want is not an integer, but just a string of exactly six decimal digits:

<xs:attribute name="ID">
  <xs:simpleType>
    <xs:restriction base="xs:token">
      <xs:pattern value="\d{6}"></xs:pattern>
    </xs:restriction>
  </xs:simpleType>
</xs:attribute>

To define a subtype of integer that allows at most six digits, you can change {6} to {1,6} in the pattern above, or use a maxExclusive of 1000000, or set totalDigits to 6.

All this assumes that your problem is defining the datatype, not imposing the uniqueness constraint.